The objective of this project is to examine the structure and function of interneurons in the reticulospinal system controlling escape behavior in fishes. The neural circuit which triggers escape behavior is simple, involving relatively few cell types and cell numbers, making this an appropriate system to use as a case study in the reticulospinal control of locomotion. Several major goals of this project are to determine the neural components of the reticulospinal system for escape in zebrafish and to examine the functions of several classes of interneuron, commissural interneurons and descending interneurons, during the escape behavior. Cell ablation and in vivo calcium imaging with confocal microscopy will be used to address these goals. Larval zebrafish will be used as a model system for this study. They are ideal due to the near transparency of their bodies and the wealth of knowledge available on all aspects of their biology. This project will provide basic information on zebrafish neurobiology and on the roles of interneurons in reticulospinal systems.